This invention relates to the production of colored polymers, and, more specifically, to measuring color thereof.
Modern plastics are typically formed of one or more base polymers or resins, one or more colorants, and other additives including, for example, fiberglass for structural reinforcement, flame retardants, plasticizers, or mold release agents. The plastics are manufactured by initially mixing these components, usually by machine, to form a substantially homogeneous polymer mixture or blend. The blend then undergoes extrusion to form a raw product which may be in the exemplary form of pellets which are in turn used by manufacturers to produce final, finished polymer products of various forms and configurations.
Experience has shown that the color of the final product may depend on several factors including the concentration and type of colorant and base resin, temperature history during mixing, and the ultimate degree of constituent inter-mixing achieved during processing. Thus, variations in color between otherwise similar polymer products may arise for a variety of reasons.
For example, color may vary among polymer products due to polymer product formulation or recipe differences. Color variations may exist between lots for a given product formulation or recipe due to machine-to-machine differences. Color differences may exist within lots due to changing raw material characteristics, changing operating conditions, and inaccuracies and other anomalies in processing including speed rates.
Plastics including thermoplastic or thermoset polymers may be used in various commercial products. Typical industries include printing, painting, fabrics, and plastics, wherein accurate color of the final polymer product is important.
Polymer color is typically adjusted by adjusting the amount of colorant for a given production run. The colorant may take any conventional form which affects the color of the polymer product by itself or in combination with other constituents. For example, solid pigments and liquid pigments or dyes may be used for effecting the color of the final product.
In a typical production process, the colorant and base resin are blended together and compounded or extruded in a laboratory machine to generate pellets. The pellets are then injection molded to obtain a plaque with substantially uniform color, which is then conventionally measured in a laboratory spectrocolorimeter. The measured plaque color is compared with a reference or standard plaque color, and differences therebetween are corrected by adjusting the colorant. The sequence is repeated until the plaque color falls within an acceptable range to the reference plaque.
A sample of the finally corrected colorant and resin blend is then compounded on a production scale machine which follows a similar procedure as the laboratory machine to produce a color plaque which is again compared with the reference plaque. If required, the colorant in the production machine is suitably corrected to effect an acceptable match between the measured plaque and the reference plaque.
This process, therefore, requires many steps to achieve a desired color in the polymer pellets which increases processing time and cost.
Accordingly, it is desired to improve the process of measuring and adjusting color in the production of a polymer product from base resins and colorants.